A torsion beam suspension generally has a torsion beam disposed between a pair of right and left trailing arms disposed in the lateral direction of the vehicle.
A trailing arm includes right and left portions when an upper member in a U-shaped cross section is mounted on a vehicle and a lower member disposed to close the opening of the U-shaped cross section. A hollow structure is formed by the right and left portions of the upper member and the lower member, and a central portion of the upper member is configured as a torsion beam (see Patent Literature 1).